Unmodified thermoplastic polyamides, particularly nylons, are generally regarded as "tough" resins. These polymers have good elongation, high energy at break, high tensile impact strength and high energy absorption. Polyamides, however, are deficient with respect to resistance to crack propagation, as reflected in notch sensitivity, brittle breaks and occasional catastrophic failure of molded or extruded parts. The tendency of polyamides to break in a brittle manner limits their utility. On the other hand, prior thermoplastic elastomer systems are known which solve some of the deficiencies noted for polyamides. However, such systems have limitations with regard to properties such as heat distortion or flexural modulus.
Much effort has been given to improving this deficiency of polyamides in general. For example, U.S. Pat. No. 4,174,358 discloses a toughened multi-phase thermoplastic polyamide composition. This patent discloses admixing at least one thermoplastic polymer with a polyamide. The thermoplastic polymer has a particle size of 0.01 to 3.0 microns and a tensile modulus of no greater than 20,000 psi. The polymer is derived from one or more monomers which are copolymerized. The patent does not disclose improved low temperature toughness as measured by low temperature notched Izod testing.
The prior art has evidenced this effort of improving impact strength of polyamides by admixing a wide variety of additives with polyamides. Some improvement in toughness has been obtained by these various additives, however, none has demonstrated significant improvement in low temperature toughness along with high impact strength without significant loss of heat deflection temperature. For example, British Patent No. 998,439 discloses a thermoplastic composition comprising a mixture of 50 to 99 percent linear polyamide and 1 to 50 percent of an olefin copolymer, the olefin copolymer containing from 0.1 to 10 mole percent of acid groups.
British Patent No. 1,279,836 discloses synthetic hair derived from polyamides and highly crosslinked copolymers which are derived from a monoethylenically unsaturated monomer and a di- or tri- ethylenically unsaturated crosslinking agent. The particle size of these crosslinked copolymers are preferably 1 micron or less.
U.S. Pat. No. 4,321,337 discloses coextruding an ionomer resin with a polyamide.
U.S. Pat. Nos. 3,373,222 and 3,373,223 disclose admixing a polyolefin and a carboxylated polyethylene with a linear polyamide. There is no disclosure relating to the particle size of the polymers added, nor to the additive polymers being made from two or more polymers.
U.S. Pat. No. 3,845,163 discloses blends of 60 to 85 percent by weight polyamide and an acid containing olefin polymer in which the acid is derived from an alpha, beta ethylenically unsaturated carboxylic acid and in which at least 10 percent of the acid groups have been neutralized with metal ions to form ionomers. This patent, however, is directed to improving weldline toughness which is not specifically related to blend toughness.
U.S. Pat. No. 4,148,846 discloses a combination of an amine reactive moiety containing polymer grafted to a polycarbonamide. This patent is directed to improving the extrudability, blow moldability and injection moldability of polyamides. While the patent does disclose improved impact strength, there is no disclosure relating to low temperature toughness. This patent discloses achieving its objectives by employing a modifier that comprises a first phase elastomeric polymer combined with a final rigid thermoplastic polymeric phase containing amine reactive moieties which are grafted to the polyamide.
U.S. Pat. No. 3,676,400 discloses polyamides having improved impact strength by blending 10 to 50 weight percent of an olefin polymer containing 1 to 10 mole percent of groups from an unsaturated carboxylic acid with 50 to 90 weight percent of a polyamide having a molecular weight of at least 10,000. This patent requires employing a polyamide having a high content of amine end groups.
U.S. Pat. Nos. 4,314,929 and 4,105,709 disclose various filled polyamide compositions which also include impact modifiers.
U.S. Pat. No. 4,167,505 discloses an impact modifier for polyamides which is produced by first forming an impact modifier concentrate of an acrylic impact modifier combined with a high molecular weight aliphatic polycarbonamide followed by mixing 10 to 30 parts by weight of the concentrate with 70 to 90 parts by weight of a low molecular weight aliphatic polycarbonamide.
None of the foregoing disclosures are with, nor demonstrate, improved low temperature toughness for polyamides in general and particularly nylon type polyamides, neither have they provided any information regarding heat deflection temperatures.